What is the difference between a class and a function in C plus plus?

You cannot point at a class, you can only point at an instance of a class, which is simply another term for an object. The class is essentially the object's type; it define's the object's behaviour, but is not the object in and of itself. The class also defines a pointer's type, so we can point at instances of a class and access the the object it represents through indirection.